1. Field of the Invention
The present invention relates to an exhaust control device for an internal combustion engine which controls the discharge of combustion gases from the interior of the cylinder bore, and more particularly relates to an exhaust control device for an internal combustion engine which controls the discharge of combustion gases from the interior of the cylinder bore in an internal combustion engine equipped with an electromagnetic driving mechanism that uses electromagnetic force to drive the valves that open and close the combustion chamber.
2. Description of the Related Art
Electromagnetic driving mechanisms that perform direct driving by means of electromagnetic force instead of using a mechanism consisting of a cam shaft, timing belt and the like have been developed as mechanisms that drive the intake valves that open and close the intake ports that conduct intake air into the combustion chambers of internal combustion engines, and the exhaust valves that open and close the exhaust ports that discharge combustion gases from such combustion chambers.
For example, the engines disclosed in Japanese Patent Application Laid-Open No. H10-141028, Japanese Patent Application Laid-Open No. H8-189315 and the like are known as internal combustion engines equipped with such an electromagnetic driving mechanism. In the electromagnetic driving mechanisms disclosed in these patents, when the piston is lowered through the cylinder bore during the intake stroke, the intake valve is driven in the valve-opening direction by an electromagnetic force at a specified timing, so that the intake port is opened and fresh air is supplied to the cylinder bore and interior of the combustion chamber via this intake port.
Furthermore, when the piston rises through the cylinder bore during the exhaust stroke, the exhaust valve is driven in the valve-opening direction by an electromagnetic force at a specified timing, so that the exhaust port is opened, and burned gases (exhaust gases) are discharged into the atmosphere from this exhaust port via the exhaust manifold (exhaust passage).
In the driving by means of this electromagnetic force, the opening-and-closing timing of the intake valve and exhaust valve can be freely set, so that the maximum volumetric efficiency can theoretically be obtained throughout the entire rotational region of the engine.
In the exhaust stroke of the engine, the residual pressure of the combustion gases inside the cylinder bore is (for example) approximately 0.6 MPa. Accordingly, when the combustion gases are discharged, the electromagnetic driving mechanism must generate a large electromagnetic force in order to overcome the pressure of these combustion gases and drive the exhaust valve in the valve-opening direction.
Specifically, in order to overcome the pushing force exerted by these combustion gases in the valve-closing direction, and thus open the exhaust valve, the electromagnetic driving mechanism on the exhaust valve side must be increased in size compared to the electromagnetic driving mechanism on the intake valve side, or else the driving current that is supplied must be increased, so that the size of the device as a whole is increased.
Furthermore, since this electromagnetic driving mechanism on the exhaust valve side cannot be used in common with the electromagnetic driving mechanism that drives the intake valve, the cost of the device is increased.
The present invention was devised in light of the abovementioned problems encountered in the prior art; it is an object of the present invention to provide an exhaust control device for an internal combustion engine which can accomplish the opening-and-closing driving of the exhaust valve by means of an electromagnetic force securely and accurately at a specified timing, without increasing the size or cost of the apparatus.
The exhaust control device for an internal combustion engine provided by the present invention is an exhaust control device for an internal combustion engine comprising a piston that performs a reciprocating motion between top dead center and bottom dead center inside a cylinder bore, an intake valve and exhaust valve that open and close a combustion chamber positioned above the cylinder bore, an electromagnetic driving mechanism which performs opening-and-closing driving of at least the exhaust valve by means of an electromagnetic force, and an exhaust passage which conducts the exhaust that is discharged by the opening of the exhaust valve, which is characterized in that this exhaust control device has a bypass exhaust passage that communicates between the cylinder bore and the exhaust passage in the region of bottom dead center of the abovementioned piston.
In the abovementioned construction, when the piston is positioned in the region of bottom dead center in the exhaust stroke in which the piston moves from the region of bottom dead center to the region of top dead center, combustion gases at a relatively high pressure are discharged into the exhaust passage via the bypass exhaust passage.
Accordingly, the pressure of the combustion gases pushing the exhaust valve in the valve-closing direction is correspondingly reduced, so that the exhaust valve can be securely driven in the valve-opening direction at a specified timing by the subsequently applied electromagnetic force.
Furthermore, the exhaust control device for an internal combustion engine provided by the present invention is an exhaust control device for an internal combustion engine comprising a piston that performs a reciprocating motion between top dead center and bottom dead center inside a cylinder bore, an intake valve and exhaust valve that open and close a combustion chamber positioned above the cylinder bore, an electromagnetic driving mechanism which performs opening-and-closing driving of at least the exhaust valve by means of an electromagnetic force, and an exhaust passage which conducts the exhaust that is discharged by the opening of the exhaust valve, which is characterized in that this exhaust control device has a bypass exhaust passage that communicates between the cylinder bore and the exhaust passage in the region of bottom dead center of the abovementioned piston, and a control valve that controls the opening and closing of this bypass exhaust passage.
In the abovementioned construction, when the piston is positioned in the region of bottom dead center in the exhaust stroke in which the piston moves from the region of bottom dead center to the region of top dead center, combustion gases at a relatively high pressure are conducted to the upstream side of the control valve via the bypass exhaust passage. Then, as a result of this control valve opening at a specified timing, the cylinder bore and exhaust passage are caused to communicate with each other, so that the above-mentioned combustion gases are discharged into the exhaust passage.
Accordingly, the pressure of the combustion gases pushing the exhaust valve in the valve-closing direction is correspondingly reduced, so that the exhaust valve can be securely driven in the valve-opening direction at a specified timing by the subsequently applied electromagnetic force.
Furthermore, the sucking through of fresh air or the like in the intake stroke can be prevented by opening the control valve only during the exhaust stroke.
In the abovementioned construction, a construction may be employed in which the control valve is a check valve that allows the flow of gases only from the cylinder bore toward the exhaust passage.
In the abovementioned construction, since the control valve is a check valve, the combustion gases (exhaust gases) discharged toward the exhaust passage from the cylinder bore are prevented from flowing back toward the cylinder bore. As a result, the discharge of combustion gases is securely performed.
In the abovementioned construction, a construction may be employed in which the control valve is driven in the valve-closing direction by a preset specified urging force.
In the abovementioned construction, when the pressure of the combustion gases inside the cylinder bore reaches a specified level or greater, the control valve is moved in the valve-opening direction by the pressure of the combustion gases against the urging force that closes the control valve. As a result, a portion of the combustion gases is discharged, so that the application of a combustion gas pressure exceeding a specified level to the exhaust valve can be prevented, and the exhaust valve can be securely driven in the valve-opening direction at a specified timing.
In the abovementioned construction, a construction may be employed in which opening-and-closing driving of the control valve is accomplished by means of control signals that correspond to the operating conditions of the internal combustion engine.
In the abovementioned construction, the opening-and-closing operation of the control valve is accomplished in accordance with the operating conditions of the internal combustion engine. Accordingly, the opening-and-closing timing of the control valve and the timing at which high-pressure combustion gases are discharged via the bypass combustion passage can easily be set at a desired timing, so that fine exhaust control can be performed in accordance with the operating conditions of the internal combustion engine.